Conventional practice for testing or inspecting the roundness of ball bearings includes mechanical sorting gauges and stylus profiling. Conventional practice also includes the use of optical inspection systems, in particular optical imaging systems.
However, these conventional techniques all suffer from problems relating to a significant amount of time required to inspect a given piece, inaccuracy, a requirement that a production line be interrupted to accomplish the inspection, and/or that only spot checking of a manufactured lot be accomplished.
Visible-wavelength interferometers are widely employed for high precision displacement measurement and surface profilometry. These interferometers generally include either single wavelength or dual wavelength optical sources.
As described in U.S. Pat. No. 4,832,489, issued May 23, 1989, to J. C. Wyant et al., a two-wavelength phase-shifting interferometer employs two laser sources for reconstructing steep surface profiles, such as aspheric surfaces. A 256.times.256 detector array is used and the technique computes an equivalent phas independently for each detector.
In an article entitled "Contouring Aspheri Surfaces Using Two-Wavelength Phase-Shifting Interferometry" by K. Creath, Y. Cheng, and J. Wyant, Optica Acta, 1985, Vol. 32, No. 12, 1455-1464 there is described two-wavelength holography using an argon-ion laser and a He-Ne laser. An uncoated aspheric surface was placed in one arm of an interferometer and two synthetic wavelengths were employed to generate interferograms that were recorded using a 100.times.100 diode array.
In an article entitled "Two-wavelength scanning spot interferometer using single-frequency diode lasers" by A. J. de Boef, Appl. Opt., Vol. 27, No. 2, Jan. 15, 1988 (306-311) there is described the use of two single frequency laser diodes to measure the profile of a rough surface. The inner surface of a spherically shaped aluminum bowl was measured by this technique and the results of the measurement were graphically compared to results obtained from a mechanical profilometer.
In an article entitled "Two-Wavelength Speckle Interferometry on Rough Surfaces Using a Mode Hopping Diode Laser" by A. Fercher, U. Vry and W. Werner, Optics and Lasers in Engineering 11, (1989) pages 271-279 there is described a time-multiplexed two-wavelength source consisting of a single mode diode that is switched between two adjacent oscillation modes.
The use of interferometry has also been extended to the testing of bearing surfaces as indicated in the following two articles.
In an article entitled "Interferometer for Measuring the Surface Shape of a Ball Bearing Raceway" by K. Nunome, M. Tsukamoto, T. Yatagai, and H. Saito, Applied Optics, 15 Nov. 1984, Vol. 24, No. 22, pp. 3791-3796 there is described an interferometric measuring technique developed to make precise measurements of periphery surface shapes, such as toroidal surfaces and raceway surfaces of bearings. The measuring apparatus consists of a Fizeau interferometer, a rotating air spindle unit, and a microcomputer system. The raceway shape along the cross section is measured at each rotating angle until the entire surface data are stored in the computer memory. The fringe data at each angle are displayed two dimensionally using a TV frame memory to obtain a peri-interferogram.
In an article entitled "Use of a Laser Interferometric Displacement-Measuring System for Noncontact Positioning of a Sphere on a Rotation Axis Through its Center and for Measuring the Spherical Contour", by P. E. Klingsporn, Applied Optics, 15 Aug. 1979, Vol. 18, No. 16, pp. 2881-2890, there is described a technique in which a laser interferometric displacement-measuring system is used for nonmechanical contact positioning of a highly reflective sphere on a rotation axis through its center and for measuring the degree of sphericity or roundness of the sphere. In one arrangement a parallel laser beam is focused to a virtual point at the center of the sphere, and in another arrangement the beam is focused at the spherical surface. It is shown on the basis of theory, and verified experimentally, that focusing the beam on the surface of the sphere is the more satisfactory arrangement. The technique was used to measure the roundness of spheres.
An optical technique that does not employ interferometry is shown in an article entitled "Optical Scanner for Ball Bearing Inspection" by R. W. Lewis, Optical Engineering, January/February 1982, Vol. 21, No. 1, pp. 113-117. This article describes a scanner that employs a fixed semicircular array of light sources to illuminate a rotating ball and an adjacent fixed array of light detectors to detect deviations from specularity on the ball surface. Each detector signal is processed by a separate channel of threshold detection electronics. The technique is said to enable inspection of balls spinning on tapered sizing railings.
However, what is not taught by this prior art, and what is thus one object of the invention to provide, is a single wavelength or multiple wavelength interferometer employed for determining a roundness of a spherical body while the body is in rolling motion through a test station, wherein a linear light pattern is projected upon a surface of the rolling body for generating a interferogram that is swept across a surface of a light sensitive detector element.
It is a further object of the invention to provide an interferometric technique employed for determining a roundness of a rotating ball bearing, the interferometer including a cylindrical lens to project a linear light pattern upon a surface of the rolling bearing.
It is another object of the invention to provide a test station for testing the roundness of a ball bearing, the test station operating in a rapid and accurate manner and further being readily integrable with a production line facility.